http://www.leangains.com/2011/03/intermittent-fasting-for-weight-loss.html
Understand the article. I may be missing some information in your situation here but the article states:
"The aforementioned studies all involve fasting, with time-intervals ranging from 18 to 36 hours. The modified ADF/CR-regimens involve one day of very low calorie intake, 300-800 kcal, followed by one day of ad libitum feeding (which means that participants were free to eat whatever they wanted)."
So super low one day with a free feeding day the next. Quite different from consecutive super low days.
Like you just said:
"Secondly, body fat percentage also matters. Lean participants lose more muscle mass than obese participants on an equal energy deficit, because body fat by itself provides a muscle-sparing effect. No need to touch the emergency funds (muscle protein) if you have money in your savings account (adipose tissue)."
I wouldn't consider you in the obese category though.
You're obviously dedicated to the cause and I commend you for it. I get 4-5 days into a good cut and am in danger of eating everything in sight. I'm surprised you can be 12-15 @80kg though. I'm estimated to be 17-18% now at 94kg. I couldn't imagine losing 14kg.
Main point is I think you're doing yourself a disservice by undergoing such a drastic cut.